Selenium is essential for the normal utilization of heme in the rat liver. Since all known biochemical functions of selenium are subserved by selenoproteins, we propose to seek a selenoprotein which influences heme metabolism. Initially we will inject rats with 75Se02-3 and identify 75Se-binding protins with standard fractionation methods. We will then purify some of them and study their heme-binding ability. Gultathione S-transferase B can block lipid peroxidation in the NADPH-microsomal lipid peroxidation system in the presence of GSH. We will seek to learn whether it does this through its function as a glutathione peroxidase by seeking fatty acid alcohols in the lipids of the system after such an incubation. We will also masure fatty acid content before and after incubation.